Virologic and immunologic factors including HIV-1 viral load, sequence diversity, virus phenotype, and titer of neutralizing antibody are relevant to the control of HIV-1 infection and disease progression. We propose to examine the role of these factors in CD4 depletion and to determine the time course of virologic and immunologic events that occur as control of HIV-1 infection diminishes and disease progresses. We will analyze serial blood specimens from selected women in the Bronx Lebanon - Mt. Sinai - Beth Israel WIHS cohort, which will reflect the racial and ethnic distribution of HIV-1 infection in women in the US. Women will be selected who display a broad range of CD4 counts, documented patterns of CD4 cell decline, and clinical status. We plan to perform focused virologic, molecular, and immunologic analyses on selected serial samples from these well-characterized women. We aim to: 1) Determine the nucleotide sequence of the principal neutralizing determinant of the HIV-1 envelope gene (V3 loop) in order to measure the degree of sequence diversity present at each time point; 2) quantitate HIV-1 cultured from peripheral blood mononuclear cells by limiting dilution and determine the relationship between the degree of diversity and viral load within single patient specimens; 3) determine the viral phenotype of serial HIV-1 isolates; and 4) study neutralization of individual HIV-1 quasispecies by assaying autologous sera. We shall examine neutralization of individual quasispecies in both cultivated virus and molecular clones of V3 loop sequences inserted into infectious vectors and shall begin to characterize the nature of the neutralization escape of the viruses which escape neutralization. We then will correlate the molecular, viral, and neutralization data with the pace of disease progression and CD4 depletion in women. These analyses are aimed at elucidating issues in HIV-1 pathogenesis, control of infection, and vaccine design; they also may identify virologic events that signal HIV-1 disease progression and serve as useful markers of impending clinical deterioration in infected individuals.